Abstract Detail

Invasive species have great ecological and economic impacts to both human society and nature, making the ability to understand and predict the invasive behavior of certain species of great import. Once introduced plant species are established in a new region, they have been frequently proven to be extremely difficult to control. Hence, preventing potential invasive species from reaching ground zero is the most economically and environmentally efficient management method. We explore the use of evolutionary distance as a quantifiable measure of predicting invasive behavior following dislocation, using the weed-rich thistle tribe, Cardueae, with the California Floristic Province, a biodiversity hotspot, as our study system. Multiple molecular phylogenies of the tribe were generated with nuclear and chloroplast DNA markers, representing the most in-depth and wide scale reconstruction of the clade to date. Branch lengths separating invasive and non-invasive exotic taxa from native California taxa were statistically compared to ascertain whether invasives are more or less closely related to natives than non-invasive introduced taxa are. Patterns within this monophyletic group show that not only are introduced thistles more closely related to natives more likely to be invasive (p<0.05), but these invasive species are also evolutionary closer to native flora than by chance. This suggests that pre-adaptive traits are more important than novel traits and/or enemy escape in determining an invader’s success. In order to examine the nature of these hypothetical ‘pre-adaptations’, the climatic niches of introduced taxa were compared. Dispersal related phenotypic traits such as pappus length and fruit weight were also analyzed. Such molecular phylogenetic approaches, coupled with ecological insights prove a fruitful means for furthering our understanding of biological invasions, and developing a predictive framework for screening potential invasive taxa.